1. Field of the Invention
The present invention relates to an air port(overfiring air port) for combustion, a method for manufacturing the air port, a boiler, a boiler facility, a method for operating boiler facility and a method for improving the boiler facility.
2. Description of the Prior Art
In a combustion furnace such as a boiler and the like, it has been required to decrease a concentration of nitrogen oxides (NOX) and to reduce unburned matter or the like. A two-stage combustion process has been applied to meet these requirements.
The two-stage combustion process is a combustion process where an incomplete combustion region (fuel-rich region) less than a stoichiometric ratio (a stoichiometric air requirement) is formed in a combustion furnace by a burner; and air making up for combustion-shortage is supplied to an inflammable gas in the incomplete combustion region by overfiring air ports (combustion air port used in a two-stage combustion). The air ports a rearranged downstream from the burner. This combustion process can curb a generation of a high temperature combustion region caused by an excess of oxygen (rich oxygen) and can reduce NOx formation. The stoichiometric ratio means that a ratio between an amount of air supplied by the burner and a stoichiometric air requirement for the complete combustion is 1:1.
In the two-stage combustion, in order to reduce the unburned matter, the promotion of mixing of the inflammable gas in the incomplete combustion region formed by the burner and air supplied from the air port is desired.
In order to satisfy such a requirement, Patent Document 1 (Japanese Patent Laid-Open No. 2001-355832) discloses that an air port is provided with a guide sleeve having a baffle. The baffle sets an injecting direction of air from the air port so as to form a straight flow of air (a primary air) in parallel with a center line of the air port and a divergent spreading flow of air (a secondary air) around the primary air are formed. According to this process, since an injection flow is spread entirely, a mixing of the inflammable gas and air in the furnace is promoted.
Patent Document 2 (Japanese Patent Laid-Open No. H10(1998)-122546) discloses an air port for injecting air with contraction flow so as to make a deeper penetration of the injected air into the furnace. Additionally, this process prevents from generating of a clinker and ashes.
In these processes, the direction of the air jet stream from the air port is fixed.    [Patent Document 1] Japanese Patent Laid-Open No. 2001-355832 (Claims and FIG. 2)    [Patent Document 2] Japanese Patent Laid-Open No. H10(1998)-122546 (Claims and FIG. 1)
A positional relationship between the incomplete combustion region formed in the furnace and the air port used as the overfiring air port in the two-stage combustion process is variously set in response to a form of the furnace. Accordingly, it is desired that an air injecting direction of the air port can be optionally adjusted in correspondence with the position of the incomplete combustion region.
In accordance with the boiler facility described in the aforesaid Patent Document No. 1, it is possible to reduce a concentration of fuel NOx and a concentration thermal NOX. However, in some kind of fuel, a concentration of carbon monoxide (hereinafter called as CO) in the combustion gas may increase. The Patent Document 1 has not described means and method for reducing the concentration of CO and for reducing concentrations of NOx and CO with better balance.